One known example of this type of lighting device is a so-called “LED in glass” device. An example is shown in FIG. 1. Typically a glass plate is used, with a transparent conductive coating (for example ITO) forming electrodes. The conductive coating is patterned in order to make the electrodes, that are connected to a semiconductor LED device. The assembly is completed by laminating the glass, with the LEDs inside a thermoplastic layer (for example polyvinyl butyral, PVB). The glass used may be safety glass. Applications of this type of device are shelves, showcases, facades, office partitions, wall cladding, and decorative lighting. The lighting device can be used for illumination of other objects, for display of an image, or simply for decorative purposes.
One problem with this type of device is that it is difficult to provide a structure which enables individual LEDs in the glass to be turned on and off, for example in order to display an image, or a dynamic pattern. This is difficult, because a two-dimensional pattern of transparent electrodes is desired, but crossovers need to be avoided if the layer structure is to be kept simple. If individual wires are used for each LED (instead of a two dimensional pattern), this results in very high wire resistances (for example ITO electrodes), leading to high electrical losses in these wires. An alternative is to place several sheets of LEDs in glass behind each other, which adds to the cost of the device.
Another problem is how to dynamically control the color of the LEDs in glass. Currently, this can again only be achieved by adding extra wires, leading again to thinner ITO wires and thus to extra electronic losses. Furthermore, LED devices are not typically suitable for ac drive voltages, as they have diode electrical characteristics.
It is an object of the invention to provide independent control of the light source devices but with a simple conductor pattern.